c(6x2)and c(4x2)reconstruction of SrTiO3(001)

In this paper we report centered 6 x 2 [c(6 x 2)] and centered 4 x 2 [c(4 x 2)] reconstructions of SrTiO3(001) surfaces observed consistently using lo w energy electron diffraction and high resolution scanning tunneling micros copy. We find that the final ordering of the SrTiO3(001) surface depends no t only on the annealing conditions, but also critically on the surface cond ition before ultra-high vacuum annealing. Auger electron spectroscopy measu rements revealed a systematic correlation of AES intensity ratio I(Sr)/I(Ti ) and I(O)/I(Ti) with various types of reconstructed surface [1 x 1, 2 x 1, c(4 x 2), and c(6 x 2)]. It also shows roughly a linear dependence of O-to -Ti ratio on the Sr-to-Ti ratio. Therefore, the change in stoichiometry dri ves the surface to different superstructures. We discuss the surface electr onic states associated with the oxygen vacancies, and their effect on the e lectron tunneling. The c(6 x 2) surface is found to be extremely stable in ultra-high vacuum, even during atomic resolution scanning tunneling microsc opic imaging. A single domain c(6 x 2) reconstruction can be stabilized on a vicinal (001) surface. (C) 1999 Elsevier Science B.V. All rights reserved .